Hao J., Moghimiardekani A., Vandewalle L., Fuentes C.A., Van Vuure A.
Construction and Building Materials, vol. 502, art. no. 144504, 2025
Natural fibre composites exhibit significant creep under hygrothermal conditions, limiting their long-term structural performance in applications such as construction and automotive. This work experimentally investigated the effects of stress levels, temperature, and relative humidity (RH), as well as their interactions, on the creep lifespan of flax fibre composites with a polyoxymethylene thermoplastic polymer matrix. Both stress level and temperature demonstrated negative effects on the creep lifespan. Interestingly, an increase in RH from 50 % to 65 % and 75 % resulted in an extended lifespan, but further increase to 85 % RH led to a significantly shorter lifespan. This non-monotonic behaviour is attributed to the opposing effects of the increased toughness due to plasticization and accelerated creep behaviour caused by the deteriorated fibre-matrix interface. Response surface methodology was used to evaluate the interaction effects. The t -test revealed that interactions between stress ratio and temperature or humidity were statistically insignificant, whereas the adverse influence of temperature on composite lifespan was mitigated at higher humidity levels, indicating a strong temperature-humidity interaction. A creep descriptor-based model was developed to estimate creep lifespan, achieving a mean absolute percentage error of 18 %. This performance is significantly better than the traditional stress ratio-based extrapolation model, which yielded an error of 194 % on the same validation data. The time-temperature superposition principle was incorporated into the creep descriptor-based model to enable lifespan predictions at low stress levels. A characteristic lifespan of 142 years was predicted for the composite subjected at a 30 % stress ratio, 23 ºC and 50 % RH. Reliability analysis indicated a 99 % probability of the composite surviving beyond 50 years. The proposed model demonstrates promising capabilities for predicting the service life of composite structures under low stress levels, which are more typical in real-world applications.
